56 Ba Barium 137.327
Alkaline earth metal s-block Period 6 Group 2

Barium

Ba · Element 56 · Alkaline earth metal

Print or save as PDF Embed on your site

Dense, reactive, and the reason a "barium meal" makes your digestive tract show up on X-rays.

State at 20°C Solid
Atomic mass 137.327 u
Electron configuration[Xe] 6s²
55Cs All 118 57La

Structure

The barium atom

Not a diagram of dots on rings — a Monte-Carlo sample of the actual probability density |ψ|² for each occupied subshell. Drag to rotate. Blue and violet mark opposite signs of the wavefunction, which is what makes bonding possible.

Orbital cloud

Measured values

Property sheet

Every bar shows where barium sits among all 118 elements for that property.

Physical

Density 3.51 g/cm³ 25%
Melting point 1000 K 43%
Boiling point 2170 K 46%
Specific heat 0.204 J/g·K
Thermal conductivity 18.4 W/m·K 46%

Atomic

Atomic radius 222 pm 78%
Covalent radius 215 pm
Van der Waals radius 268 pm

Electronic

Electronegativity 0.89 4%
Ionisation energy 502.7 kJ/mol 5%
Electron affinity 14.5 kJ/mol 16%

Occurrence

Abundance in crust 425 mg/kg 88%

Identity

SymbolBa
Atomic number56
Atomic mass137.327 u
CategoryAlkaline earth metal
Blocks
Crystal structurebody-centered cubic
Oxidation states+2
Discovered1808
Discovered byHumphry Davy

Sources: IUPAC 2021 standard atomic weights · CRC Handbook of Chemistry and Physics · NIST. Values marked ~ are predicted rather than measured.

Same element, different neutrons

Isotopes of barium

All barium atoms have the same number of protons, 56, and differ only in their number of neutrons: those variants are its isotopes. The most common, Ba-138, has 82 neutrons and makes up 71.70% of natural barium.

Isotopes of barium found in nature, with their share of the natural element, and well-known radioactive ones
ISOTOPE Neutrons Natural Abundance Half-life Decay Mode
Ba-130 74 0.11% Stable —
Ba-132 76 0.10% >3.0 × 10²¹ yrs 2β⁺
Ba-133 77 — 10.551 yrs ε
Ba-134 78 2.42% Stable —
Ba-135 79 6.59% Stable —
Ba-136 80 7.85% Stable —
Ba-137 81 11.23% Stable —
Ba-138 most common 82 71.70% Stable —

The classroom shortcut, rounded atomic mass minus atomic number, gives 81 for barium, but the most common barium atom has 82 neutrons: the atomic mass, 137.327, is an average over all natural isotopes.

Decay modes

2β⁺
double positron emission
ε
electron capture

Data: IAEA Nuclear Data Section, LiveChart of Nuclides, ground-state evaluations, retrieved October 10, 2026. Abundance is the share of atoms in the natural element; a dash means the isotope has no standard natural abundance.

Size, to scale

How big is a barium atom?

Radius 222 pm — that is 0.222 nm, so about 2.25 million of them side by side would span a millimetre.

Thermal range

Solid, liquid, gas — and when

Barium is liquid over a 1170 K window, from 1000 K to 2170 K.

Where it sits

Position in the table

Barium sits in period 6, group 2. Everything in group 2 shares the same outer-electron count, which is why they behave so similarly.

Other alkaline earth metals

4Be 12Mg 20Ca 38Sr 88Ra
All alkaline earth metals

The story

What barium is, and how we found it

Dense, reactive, and the reason a "barium meal" makes your digestive tract show up on X-rays.

The discovery of barium

The Alchemist's Glowing Stone

The barium story begins in early 1600s Italy with Vincenzo Casciarolo, a Bologna shoemaker and amateur alchemist. While searching for the philosopher's stone, he discovered strange heavy stones near Bologna that, after heating, glowed eerily in the dark. These "Bologna stones" (barium sulfide) fascinated scholars for centuries before anyone understood their true nature.

Scheele's Chemical Detective Work

In 1774, Swedish pharmacist Carl Wilhelm Scheele made the crucial breakthrough while analyzing pyrolusite (manganese dioxide). He discovered that some samples contained an unknown "heavy earth" that formed a white precipitate with sulfuric acid - the first chemical evidence of barium's existence.

Hope's Systematic Investigation

Scottish physician Thomas Charles Hope at the University of Glasgow systematically studied this mysterious substance in 1792. Guyton de Morveau named the earth "barote", and Lavoisier changed it to "baryte" (Latin baryta), from the Greek "barys" meaning heavy, recognizing its unusually high density compared to other earth-like substances.

Davy's Electrolytic Triumph

The brilliant English chemist Sir Humphry Davy finally isolated metallic barium in 1808 using his important electrolysis technique. By passing electric current through molten barium hydroxide, he produced silvery droplets of pure barium metal - though they immediately burst into flames upon contact with air.

Dangerous Early Experiments

Early barium researchers faced constant danger. The metal's high reactivity caused numerous laboratory fires and explosions.

Industrial Revolution Applications

The 19th century saw barium transition from laboratory curiosity to industrial workhorse. Barite mining expanded rapidly as the oil industry discovered its value in drilling muds. The invention of X-rays in 1895 created new medical applications, while the growth of electronics in the 20th century made barium titanate essential for modern capacitors.

Modern Recognition

Today, barium honors its discoverers through the Scheele Award in analytical chemistry and the Davy Medal from the Royal Society. From glowing stones to smartphone components, barium's journey reflects humanity's evolving understanding of matter itself.

Applications

What barium is used for

Medical Imaging

Barium sulfate has transformed medical diagnostics as the primary contrast agent for X-ray imaging of the digestive system. Its high atomic number makes it opaque to X-rays, allowing doctors to visualize the stomach, intestines, and colon with remarkable clarity. Over 10 million barium studies are performed annually worldwide, detecting cancers, ulcers, and digestive disorders that would otherwise remain hidden.

Advanced Pigments and Coatings

Barium sulfate serves as a premium white pigment and extender in high-performance paints, providing exceptional opacity, brightness, and chemical resistance. Automotive paints use barium compounds for durability and color stability, while architectural coatings rely on barium for weather resistance and fade prevention.

Oil and Gas Drilling

The petroleum industry consumes most of the world's roughly 8.7 million tons a year of barium sulfate (barite) as a weighting agent in drilling muds. This dense mineral increases mud density to counteract high-pressure oil and gas formations, preventing dangerous blowouts during deep drilling operations reaching depths of 30,000+ feet.

Display Technology

Barium titanate transformed electronics with its ferroelectric properties, enabling capacitors that store massive charge in tiny spaces. CRT televisions and computer monitors used barium compounds in electron guns and phosphor coatings, while modern ceramic capacitors in smartphones contain barium titanate for power management.

Pyrotechnics and Flares

Barium nitrate and chlorate create brilliant green flames in fireworks, flares, and military signal devices. The distinctive green color is so pure and bright that barium compounds are irreplaceable in professional pyrotechnics, from Olympic ceremonies to emergency maritime flares.

Glass and Ceramics Enhancement

Optical glass containing barium oxide achieves exceptional clarity and refractive properties for precision lenses in cameras, telescopes, and scientific instruments. Crown glass with barium provides superior optical performance while ceramic applications use barium for enhanced dielectric properties.

Medical Procedures

If you've ever had a "barium swallow" or digestive X-ray, you've consumed barium sulfate. This chalky, strawberry-flavored drink allows doctors to see your digestive tract clearly on X-rays, helping diagnose everything from ulcers to intestinal blockages safely and effectively.

Automotive Industry

Your car's paint likely contains barium sulfate for durability and shine. Brake pads use barium compounds for consistent friction, while spark plug ceramics incorporate barium for heat resistance. Even automotive glass may contain barium for optical clarity.

Household Products

Premium paints and primers in your home contain barium sulfate for superior coverage and longevity. High-end cosmetics use barium sulfate as a safe, low-toxicity filler and brightening agent in foundations and powders.

Electronics

Your smartphone, tablet, and laptop contain barium titanate capacitors that manage power efficiently. These tiny components store and release electrical energy precisely, enabling fast charging and stable operation of modern electronic devices.

Construction Materials

Concrete and building materials often include barium sulfate for radiation shielding in hospitals and nuclear facilities. Dense barium concrete protects medical staff during X-ray procedures and shields nuclear reactor facilities.

Photography and Optics

High-quality camera lenses and binoculars use barium-containing optical glass for superior image quality. The barium oxide reduces chromatic aberration and provides exceptional clarity for professional photography and scientific instruments.

Security Features

Paper money and important documents sometimes incorporate barium compounds in security inks and papers, making counterfeiting more difficult through special detection methods available to authentication experts.

Where it comes from

Natural occurrence

425 mg/kg of Earth's crust · more abundant than 88% of elements

Abundant Crustal Element

Barium ranks as the 14th most abundant element in Earth's crust at 425 parts per million, making it more common than carbon or sulfur. Despite this abundance, barium never occurs as a free metal in nature due to its high reactivity with oxygen and water.

Primary Mineral - Barite

The most important barium mineral is barite (BaSO₄), forming massive deposits worldwide. Major barite mines operate in China, India, Morocco, and the United States, with India (about 3.0 million tons in 2025) and China (about 2.2 million tons) together supplying roughly 60% of global output.

Hydrothermal Origins

Hydrothermal processes create most commercial barite deposits when hot, mineral-rich fluids precipitate barium sulfate in veins and cavities. These deposits often associate with lead, zinc, and fluorite minerals, creating complex ore bodies that challenge mining operations.

Witherite - The Rare Carbonate

Witherite (BaCO₃) forms beautiful crystal clusters but occurs much less frequently than barite. Named after British mineralogist William Withering, these formations provide high-purity barium for specialized chemical applications requiring carbonate starting materials.

Sedimentary Concentrations

Marine environments concentrate barium through biological processes, creating sedimentary barite deposits on ocean floors. Deep-sea drilling reveals barium-rich layers that record ancient oceanic conditions and biological productivity cycles.

Geographic Distribution

Significant barium deposits span the globe: Nevada's Battle Mountain (world's largest barite mine), India's Andhra Pradesh (high-grade deposits), Morocco's Atlas Mountains (major reserves), and Turkey's Anatolian region (growing production).

Stellar Formation

Barium forms in asymptotic giant branch stars through the s-process, where slow neutron capture builds heavy elements. Barium-enhanced stars provide astronomical laboratories for studying nucleosynthesis and galactic chemical evolution over billions of years.

Handling

Safety

Severe Toxicity Warning

POISON: Soluble barium compounds are extremely toxic. Barium chloride, nitrate, and hydroxide can cause fatal poisoning; as little as 0.8 gram of barium chloride may be fatal. Symptoms include vomiting, diarrhea, muscle paralysis, heart arrhythmias, and respiratory failure leading to death.

Cardiovascular Dangers

Barium poisoning primarily affects the cardiovascular and nervous systems. It blocks potassium channels in cell membranes, causing dangerous heart rhythm abnormalities, muscle weakness, and paralysis. Emergency treatment requires immediate potassium supplementation and cardiac monitoring.

Safe Compound Exception

Barium sulfate is remarkably safe due to its complete insolubility in water and biological fluids. Used safely in millions of medical X-ray procedures, it passes through the digestive system unchanged. However, never confuse it with soluble barium salts which are deadly.

Radioactive Barium Hazards

Barium-140 and other radioactive isotopes pose dual threats from both chemical toxicity and radiation exposure. These isotopes concentrate in bones like calcium, causing long-term radiation damage and increased cancer risk.

Metallic Barium Reactivity

Metallic barium oxidizes quickly in air, is a flammable solid, and reacts vigorously with water, producing hydrogen gas and caustic barium hydroxide. Store under inert gas or mineral oil. Metal fires require special extinguishers - never use water.

Emergency Procedures

For barium poisoning: immediate medical attention is critical. Do not give activated charcoal, which does not bind barium; call emergency services or poison control at once, and in hospital oral sodium or magnesium sulfate may be given to turn the barium into insoluble barium sulfate. Induce vomiting only if instructed by poison control, and expect cardiac monitoring and potassium therapy in hospital. Contact emergency services immediately - minutes can mean the difference between life and death.

Workplace Safety

Industrial workers handling barium compounds must use full respiratory protection, chemical-resistant gloves, and eye protection. Maintain strict hygiene protocols, shower after exposure, and never eat or drink in work areas containing barium materials.

Keep exploring

Use barium in the tools

Quick answers

Barium: common questions

What is barium?

Barium (symbol Ba) is element 56 on the periodic table, an alkaline earth metal in period 6, group 2. Dense, reactive, and the reason a "barium meal" makes your digestive tract show up on X-rays. At room temperature it is a solid.

What is the electron configuration of barium?

Barium's ground-state electron configuration is [Xe] 6s², giving 6 occupied shells with the distribution 2, 8, 18, 18, 8, 2.

What are the melting and boiling points of barium?

Barium melts at 1000 K (726.9 °C) and boils at 2170 K (1896.9 °C).

What is the atomic mass of barium?

The standard atomic weight of barium is 137.327 u. That is a weighted average across its naturally occurring isotopes, which is why it is rarely a whole number.

How many neutrons does barium have?

The most common barium atom, Ba-138, has 82 neutrons: its mass number, 138, minus its atomic number, 56. It makes up 71.70% of natural barium. The classroom shortcut, rounded atomic mass (137.327) minus atomic number, gives 81 instead, because the atomic mass is an average over all natural isotopes of barium.

How dense is barium?

Barium has a density of 3.51 g/cm³. Water is 1.0 g/cm³, so a block of barium is about 3.5× heavier.

What is the electronegativity of barium?

Barium has a Pauling electronegativity of 0.89. The scale runs from 0.70 (francium, the least greedy for electrons) to 3.98 (fluorine, the most). A value this low means it readily gives its outer electrons away, forming positive ions.

Who discovered barium, and when?

Barium was discovered in 1808 by Humphry Davy. Origin of the name: Greek barys, "heavy".

How common is barium on Earth?

Barium makes up about 425 mg/kg of the Earth's crust — common enough to be mined at scale.

← Previous Cs Cesium Element 55 · Alkali metal Next → La Lanthanum Element 57 · Lanthanide